Download Development of Joints

Sukumal Chongthammakun,Ph.D.
Department of Anatomy
Faculty of Science, Mahidol University
Email: [email protected]
http://intranet.sc.mahidol/AN/
Germ layer contribution
Chondrogenesis
• Begins week 5
• Condensation and differentiation
• Centers of chondrification
• Secretion of the extracellular matrix
• Entrapment of chondroblast
• Formation of chondrocyte
Growth of cartilage
Interstitial growth
Appositional growth
Osteogenesis
Mechanism of bone formation
•
Endochondral ossification
•
Intramembranous ossification
Endochondral ossification
• Ossification begins at the start of fetal period (mo. 3)
• Perichondrium differentiates into a layer of
osteoprogenitor cells
• Differentiation into osteoblasts and secretion of
a layer of osteoid
• Calcification and forming a bony collar
• In the center, cells of the cartilage hypertrophy and
degenerate
• Penetration by the vascular bud
Intramembranous ossification
•
Condensations of mesenchymal cells
• Secretion of osteoid
• Spicules are formed
• Networks of trabeculae
• Entrapment of osteocytes
The Axial Skeleton
1. The vertebral column
2. The attached rib
3. The sternum
4. The skull
Vertebrae and ribs are formed by endochondral
ossification of the sclerotome regions of somites
•
Sclerotome cells surround the developing neural tube
• Ventral portion forms body(centrum) around the notochord
• Dorsal portion forms costal processes laterally
(T1-12 : articulate with ribs)
• Intervertebral disks are formed
• Notochord remains as the nucleus pulposus
• The fibrocartilage is formed around N. pulposus
(Annulus fibrosus)
All somites contribute to the formation of
the axial skeleton of the body and head
42 to 44 pairs of somites develop
• 4 occipital (1 degenerates)
• 8 cervical
• 12 thoracic
• 5 lumbar
• 5 sacral
• 8-10 coccygeal (last 5-7 degenerate)
Development of the skull
Neurocranium
•
membranous neurocranium
•
cartilaginous neurocranium
Viscerocranium
•
membranous viscerocranium
•
cartilaginous viscerocranium
Membranous Neurocranium
Cartilaginous Neurocranium
Membranous Viscerocranium
Cartilaginous Viscerocranium
Appendicular Skeleton
• Somatic lateral plate mesoderm forms the skeleton
of the appendages : the limb bones and appendicular
girdles
• The appendicular skeleton is formed by
endochondral ossification of cartilage models
Development of the Joints
Synovial Joints
interzonal mesenchyme differenciates :
1. Peripherally: to capsular and other ligaments
2. Centrally: disappears and becomes the joint cavity
3. Where it lines the capsule and articular surfaces:
forms the synovial membrane
Development of the Joints
Cartilaginous Joints
Interzonal mesenchyme differenciates into:
• Hyaline cartilage eg. Costochondral joints
• Fibrocartilage eg. Symphysis pubis
Development of Joints
Fibrous Joints
Interzonal mesenchyme differenciates into:
• Dense fibrous connective tissue
eg. Sutures of the skull
Embryonic features unique to the limbs
• Limbs form by “budding” out from the
ventrolateral body surface.
• Limbs are formed by ectoderm covering a
solid mesoderm core, with no endoderm
contributions. There is no coelom.
Germ layer origins of the limbs
1. Somatic lateral plate mesoderm: cartilage, bone & CNT
2. Skeletal muscle is outsider migrating in from the somites.
3. Surface ectoderm: epidermis of skin & its specialization
4. Nerves & blood vessels grow in from the body using
connective as a guide.
Limb mesoderm and
surface ectoderm interaction
1. Limb mesoderm induces surface ectoderm to form
“apical ectodermal ridge (AER)”.
2. AER induces mesoderm underneath to continue
proliferation then commit to specific derivatives.
3. Limb mesoderm also induces the formation of limbspecific mesoderm specializations eg. Nails.
Proximal-Distal Limb Axis
• Directed by AER
• The first deposit is programmed to form humerus
• The last deposit is programmed to form the bones
of phalanges
Dorsal-Ventral Limb Axis
• Dorsal side is continuous with the dorsal side
surface of the body.
• Ventral side is continuous with the ventral side
surface of the body.
Cranial-Caudal Limb Axis
• is established by a gradient of inducing signals released
from cells of the “zone of polarizing activity (ZPA)”
• The most caudal bones (eg. Little finger) form in response
to exposure to a maximum of inducer.
• The most cranial bones (eg. Thumb) form in response to
exposure to the lowest concentration of inducer.
• Retinoic acid may be the ZPA inducer
Constriction and Regression
Limb buds appear at the end of week 4 and the
beginning of week 5 and become externally
constricted into regions by week 8
Week 6 :
Formation of the hands and footplates (circumferential
constriction)
Week 7-8 :
Formation of finger and toe rays (longitudinal
constriction)
Week 8 :
Formation of 2nd circumferential constriction
Rotation
Final feature of limb development : Limbs rotate
about their long axis.
The arms rotate 90o dorsolaterally
The legs rotate 90o ventrolaterally
Rotation of the limbs results in :
1. The final orientation of the joints
2. The final location of muscle groups.
3. The mature patterns of sensory innervation of
the skin called “dermatome”.
Histogenesis of skeletal muscle
• Germ layer origins :
All skeletal muscle is derived from somitic myotomes
• Connective tissue directs muscle mass formation
• Formation of multinucleated skeletal muscle cells
occurs by fusion of myoblasts with each other.
• Skeletal muscle cell fusion, formation of contractile
machinery, and specific fiber types do not require
nerve input.
Distiguishing between trunk, head and
limb muscles
1. Trunk muscles form directly from myoblasts
remaining in the myotomes.
2. The cells that migrate form intrinsic limb muscles,
and the muscles of shoulder and pelvic girdles.
3. Cells from the most cranial myotomes form head
and neck muscle after they migrtae into the
pharyngeal arches.
Innervation : the key to the origin of
skeletal muscles
Cranial nerves : muscles of pharyngeal arches
Spinal nerves : muscles of neck, body and limbs
Dorsal primary rami
Ventral primary rami
Axial muscles of the trunk
Trunk (axial) muscles form directly from myotomes.
Dorsal portion :
epimere
epaxial muscles
Ventral portion :
hypomere
hypaxial muscles
Appendage muscles:
limbs and appendicular girdles
Limb muscles and appendicular girdle muscles all
originate from myotomal cells that migrate into
the limbs.
Dorsal limb bud mases
extensors
supinators
abductors
Ventral limb bud masses
flexors
pronators
adductors
Appendage muscles:
limbs and appendicular girdles
The intrinsic limb muscles are formed from both
limb muscle masses.
All muscles of the appendicular girdles are derived
from the dorsal limb muscle mass.
Innervation:
Dorsal muscle mass :
dorsal branches of ventral 1o rami
Ventral muscle mass :
ventral branches of ventral 1o rami
Muscles of the head and neck
Precursors migrate into pharyngeal arches before
forming muscles.
Innervation helps distinguish the origins.
Origins of the Craniofacial Muscles
-------------------------------------------------------------------------------------------------------Mesodermal Origin
Muscles
Innervation
-------------------------------------------------------------------------------------------------------Somitomeres 1, 2 Superior, medial, and ventral recti
Oculomotor (III)
Somitomere 3
Superior oblique
Trochlear (IV)
Somitomere 4
Jaw-closing muscles
Trigeminal (V)
Somitomere 5
Lateral rectus
Abducens (VI)
Somitomere 6
Jaw-opening and other 2nd arch muscles
Facial (VII)
Somitomere 7
Stylopharyngeus
Glossopharyngeal (IX)
Somites 1, 2
Intrinsic laryngeals
Vagus (X)
Somites 2-5
Tongue muscles
Hypoglossal (XII)
--------------------------------------------------------------------------------------------------------
Congenital Defects of the Skull
Caused by genetic and environmental factors and disturbing
neural crest migration into/and proliferation in pharyngeal
arches
Anencephaly : failure of cranial neuropore to close in week 4.
Craniofacial synostosis : premature closure of sutures
between flat bones of neurocranium
coronal suture : oxycephaly/turricephaly
sagittal suture: scaphocephaly
Craniofacial dysostosis : underdevelopment of arch facial
bones, including maxill and mandible
Scaphocephaly
A. Oxycephaly
B. Plagiocephaly
Congenital Defects
of Vertebrae and Ribs
Hemivertebra : results in scoliosis
Spina bifida : vertebral arches fail to fuse dorsally
Congenital Defects of the Limbs
Causes : genetic/environment
Hyperthermia
Drugs eg. Aspirin, anticonvulsant dimethadione, excess RA
Achondroplasia (chondrodystrophy) : premature ossification
in epiphyseal plate of long bones
a. Short vertebral column
b. Short limbs with thick diaphyses in long bones
c. Sunken midfacial region
d. Normal to superior mental capacity
Achondroplasia
Congenital Defects of the Limbs
Amelia : complete absence of limb(s)
Meromelia : absence of segment(s) of limb(s)
Phocomelia : a form of meromelia in which proximal
structures are small or absent
Polydactyly : extra digits (incomplete and useless)
Syndactyly : fused or web digits (lobster claw)
A. Unilateral amelia
B. Meromelia
A. Syndactyly
B. Lobster claw
Congenital Defects of the Skeletal Muscles
Muscular dystrophy : a family of genetic diseases in which
there is postnatal degeneration of various muscle groups
Duchenne muscular dystrophy : caused by a lack of actinbinding protein called dystrophin
Absent or underdeveloped muscle groups :
• associated with bone defects
• unassociated with bone defects